Process and material for the preparation of printing plates



United States Patent K 22 Claims. ci. 101-1492) The present inventionrelates to a process for the preparation of printing plates, wherein thewater-accepting surface of a support is coated with a covering layeronto which a powder image is transferred and fixed by heat; the coveringlayer is then removed. The invention also relates to a material forcarrying out this process.

Printing plates with water-accepting surfaces are known. Thewater-accepting property in the non-printing areas is of greatimportance, since it renders these areas repellent to greasy ink. Theprinting areas on the other hand accept the ink, thus producing theprint image. 7

According to the prior art, water-accepting surfaces are produced byproviding supports, i.e., mechanically resistant bases the surface ofwhich is not water-accepting, particularly paper, which is the mostimportant material, and plastic materials, with a coating consisting,for example, of carboxymethyl cellulose. Powder images produced by aknown electrophotographic process are trans ferred onto printing platesprepared in this way.

The necessary fixing of the powder image is carried out with the aid ofsolvent vapors which partly dissolve the resinous powder substance andmake it adhere to the water-accepting surface. It has, however, provedto be a disadvantage, during the subsequent printing process with aprinting plate obtained in this manner, that the anchoring of the resinareas which are supposed to print is not very satisfactory. Even withmedium-long runs, portions of the image areas come off.

A firm anchoring of the powder image to the mechanically stable supportthrough fixing by heat is not possible, since the resulting heat causesfaults, i.e., cracks and shrinking, to appear in the water-acceptinglayer. During the subsequent printing process, the layer tends to acceptink in these cracks, which has a disturbing eflfect on the print imageand may even render it unrecognizable.

Furthermore, it is a disturbing factor with all fixing processes thatthose toner particles which adhere in an undesirable manner to thenon-image areas during the transfer of the powder image, are bonded tothe support during the heat-fixing process and therefore print duringthe subsequent printing process, thus producing a disturbing so-calledimage background. It has proved to be uneconomical for normalrequirements to do away with the coatings and to replace the originallyhydrophobic supports by hydrophilic materials, such as aluminum plates.Even then, the disadvantages mentioned above still apply.

The present invention achieves a firm and mechanically stable anchoringof the powder image to the support without damaging the hydrophiliclayer, particularly when using inexpensive paper supports provided witha hydrophilic layer. Furthermore, it is intended to obtain print imageswhich are practically free of background when transferring a powderimage onto any kind of support.

The present invention provides a process for preparing printing platesby transferring a powder image and using a support having a hydrophilicsurface. In this process, the hydrophilic surface is provided with acovering layer, which is soluble in a solvent which does not dissolvethe material of the hydrophilic surface, the powder image to bereproduced is transferred onto the covering layer, fixed thermally byburning-in, and the covering layer is then 3,315,600 Patented Apr. 25,1967 removed with a solvent which does not dissolve the hydrophilicsurface, thus decoating the latter.

The present invention also provides a material for carrying out theabove process. The material comprises superimposed layers which arelinked together, i.e., a support with a hydrophilic surface, on top ofwhich there is a covering layer which is soluble in a solvent which doesnot dissolve the hydrophilic surface.

By the present invention a printing plate is obtained which producesvery long runs of prints which are practically free of background. Theanchoring of the printing areas to the support is very firm due to theburning-in process and is not damaged even during very long runs. Byremoving the covering layer with water or dilute aqueous acids or, ifdesired, with aqueous alkaline solvents,

' the unaffected hydrophilic surface is decoated in the nonprintingareas. The hydrophilic surface is not attacked by the solvent removingthe covering layer, since the two coatings have diflerent solubilities.The decoated, smooth, and undamaged surface has perfect water-acceptingproperties, so that images which are practically free of background areobtained. Individual toner particles which might have been deposited onthe covering layer during the transfer process of the powder image arealmost completely removed together with the covering layer, so that theyhave no adverse influence later.

Cellulose products, such as paper which is commercially available forprinting purposes and which has a sufiicient mechanical and dimensionalstability, are suitable as supports. It is, however, also possible touse plastic foils, for example thermoplastic materials such aspolyolefins, including polyethylene and polypropylene; or polyacrylates;or polyamides; or thermosetting plastics, for example phenolformaldehyderesins, or modified natural resins, if these have a sufficiently highmechanical stability. Any other insulating materials may advantageouslybe used as supports, since the powder image to be reproduced is notproduced on the printing plate itself but by transfer of a powder image.Metal foils, such as aluminum, zinc or copper plates may also be used.Metal foils have an inherent hydrophilic surface. If materials are usedhaving a surface which is not hydrophilic, the supports must be providedwith a hydrophilic coating; coatings of this nature are known.Substances which are particularly suitable for this purpose are gumarabic, mesquite gum, karaya gum, guar gum and similar malogalactans,ammonium alginate and potassium alginate. Of the proteins, casein, soyabean protein, zein, gelatin, egg albumin and blood albumin are suitable.The following synthetic, hydrophilic colloidal substances are alsosuitable: carboxymethyl cellulose, potassium polyacrylate, carboxylderivatives of polystyrenes which have been rendered soluble by theaddition of a suitable alkali, hydroxy ethyl cellulose and polyvinylalcohol. Other suitable water-accepting, i.e., hydorphilic colloidalsubstances are starch, dextrin, and pectin and its derivatives,including fibrous potassium pectate..

The aforementioned supports which do not have an inherentwater-accepting surface are coated with the water-accepting substancesin known manner, generally from a solution, and dried. The resultingsupports with water-accepting surfaces are inexpensive and commerciallyavailable in various forms.

For the covering layer, compounds having satisfactory wateroracid-solubility, sufiicient stability to heat, and useful layer-formingproperties are suitable. If unco-ated metal supports are used, thesecompounds may also be alkali-soluble.

The following Water-soluble compounds are, for example, suitable for thecovering layer: alkali salts and alkaline-earth metal salts of organicmonoor oligosulfonic acids, particularly with aromatic or heterocyclicproperties.

nuclei, for example the potassium salt of 1,3-dihydroxynaphthalene-5,7-disulfonic acid, the sodium salt of benzenesulfonic acid, and thesodium salt of furancarboxylic acid; organic, preferably aromatic,carboxylic acids, such as the sodium salt of 4-chlorobenzoic acid, theammonium salt of 4-dimethylaminobenzoic acid, the sodium salt. of

' 4-hydroxy-toluene-2 carboxylic acid, and the postassiurn salt ofnaphthalenc-1,8-dicarboxylic acid.

If the powder images are transferred onto metal foils, for examplealuminum foils, the aluminum foils .may also be coated withalkali-soluble compounds, for example aromatic carbocyclic or aromaticheterocyclic sulfonic acids and carboxylic acids, such as benzoic acid,amino benzoic acid, picolinic acid, naphthoic acid, 'benezene j sulfonicacid, naphthalene-disulfonicacids, and quinoline- 6-sulfonic acid;compounds containing hydroxyl groups, such as resorcinol,2,3-dihydroxynaphthalene, 1,2,3-trihydroxyanthraquinone, andphloroglucinol; acid anhydrides, such as phthalic acid anhydride, andnapthalene dicarboxylic acid anhydride; sulfonamides, such asnaphthalene 1 sulfanilide, phenylsulfanilide,-(p-tolyl-sulfonamide)-acenaphthene, and sulfonimides, such as benzoicacid-o-sulfonic acid imide, and benzene-disulfonic acid (1,2) imide. Theaforementioned compounds which are used for the covering layer may alsobe applied in admixture with resins up to approximately 50% by weight;In this case, however, it is advantageous to add 'small quantities oforganic solvents to the aqueous solvents used for .decoating',

for example ethyl alcohol, isopr'opyl alcohol, glycolmonoethyl ether, ormixtures of such solvents. Mixtures of such substances with smallquantities of other substances, such as pigments or'fillers may also beused for forming the covering layer.

As resins, the following compounds are, for example,

' suitable: natural resins, such as balsam'resins, colophony,

shellac, modifiedsynthetic resins, such as colophony-modified phenolresins and other resins with a higher colophony content, and plasticmaterials, such as coumarone resins and indene resins; in particularresins which are readily soluble in solvents, for example ketone resins,maleinate resins, maleic acid-colophony mixed esters of alcohols of highmolecular weight, and phenol-formaldehyde conden- For covering layers onmetal supports, which may sates.

. also be decoated with the aid of alkaline solutions, it is,advantageous to use alkali-soluble resins, for :example 4 e 606,518; and626,060. A powder imageecorresponding to V the original is obtained.

mixed polymers of styrene and maleic acid anhydride,

maleinate resins and phenolic resins.

V The aforementioned compounds for the covering layer are applied insolution onto the hydrophilic surface of the support. 'by spraying,spreading, roller application, dipping into a solution, or applicationonto the support while rotating. The material is then dried at anelev-ated temperature.

For the production of powder images on the material according to thepresent invention, a mirror image of an original is produced in knownmanner on an electrophotographic material, such as selenium, zinc oxideoran organic coating, by contact with the original or preferably 'byepiscopic or dioscopic projection. This invisible image is developed bycontacting itwith adeveloper mixture comprising a toner, for example aresin-carbon black mixture. Preferably, developed mixturesiare usedwhich are described in Belgian Patents Nos. 594,137; 594,397;

' This may be performed in known manner aqueous acid solutions.

accepting surface is decoated in the non-image areas, but 7 The materialof the present invention is placed onto this powder image with itscovering layer and placed in the field of a corona discharge whichcauses the powder image to be transferred from the photosemi-conductivelayer onto the covering layer of the material of the present invention.obtained.

The images are then fixed by heating to 100470 0., Y

preferably to 120450 example, with an infra-red radiator. to partiallydissolve the powder image solvent vapors and to fix it by heating. 7

When converting the fixed images into a printing plate,

C.; this may be performed for by treatment with the covering layer isremoved from the non-image areas. 7

When removing the water-soluble compounds mentioned above as suitablefor the preparation of the covering layer, wiping over with pure waterwill be sufficient. When removing acid-soluble compounds, this beingparticularly important with paper printing foils, weak aqueous solutionsof acids, such as phosphoric acid, hydrochloric acid, and acetic acid,are used in concentrations up to 5% by weight. Up to 50% by Weight oforganic solvents,

such as methyl and/ or ethyl alcohol, isopropyl alcohol,

and glycolmonoethylether may also be added to these With this treatment,the waternot damaged. The areas covered by the fixed powder are notattacked.

If an alkaline medium is required for removing the covering layer.comprising the aforementioned alkalisoluble compounds, up to 5%. byweight aqueous solutions of alkali or alkaline earth hydroxides aresuitable, for example, solutions of sodium, potasssium and calciumhydroxide and alkali phosphates, in particular the sodium phosphatesandalkalipolyphosphates which exhibit an alkaline reaction in an aqueoussolution, for instance, so-

water-soluble silicates, such as dium polyphosphate; also basicsubstances may also'be sodium silicate. Organic used for this purpose.The following organic basic substances are suitable: primary, secondaryand tertiary satu 7 rated amines of low molecular weight, such astrimethyh amine, ethylamine, diethylarnine, triethylamine, and propylamine; amino alcohols, for example ethanolamine, di-

ethanolamine, N-methyldiethanolamine,

diethylenetriarnine, and triethylenetetrami'ne; and substituted acidamides of low molecular weight, for example dimethylformamide.

These organic basic substances may partly bensed undiluted. In mostcases, however, it is advisable to use them in dilution, particularlywithstro'nger bases. Preferably, solutions of 0.01 to 15 %"'by:weight,particularly of 1.0 to 5.0% are used. Suitable solvents are water and/or organic solvents, such as methyl alcohol, ethyl alcohol,

isopropylalcohol, and ethyleneglycol' monomethyletherj mixtures ofdifferent solvents may also be used. Furthermore, it is oftenadvantageous to add thickening agents to the acid as well as thealkaline liquids in order to increase the viscosity thereof. Thefollowingsubsta'rices may be used, for example, as thickeningagentszpolyvinylalcohol, cellulose products, such as-carboxymethylcellulose or alkyl cellulose, or'solnble'starch products. e

After the treatment witht'he liquids Which remove the coating from thenon-image areas, it is advantageous. but not necessary to rinse theprinting plate with water and to increase the hydrophilic propertiesthereof even further by wiping the-plate with a dilute solution ofphosphoric J acid. After inking up with greasy ink, printing may beperformed in'known manner. With the material of the present invention,high'quality printing plates which are completely free of background andproduce long runs, are obtained by the transfer method. i

Images corresponding to the original are thus It is also possibleN-ethyldiethanol amine, diamines and polyamines, such asethylenediaminep The invention will be further illustrated by referenceto the following specific examples:

Example 1 Parts by wt. Zinc oxide (Zinkoxyd besonders rein, Sorte A ofthe Zinkweiss-Handelsgesellschaft Oberare homogenized three times in acolloid mill or in a high-speed mixer. The ready-to-brush-on suspensionis applied in known manner to a paper foil, which is backed with a thinaluminum foil, and dried. For producing images on the electrocopyingmaterial produced in this manner, the coating is provided with anegative charge by means of a corona discharge, and is then exposed inthe cassette of a vertical reproduction camera with a roof" mirror for5-30 seconds, depending on the reproduction scale, at stop 9. EightNitrophot bulbs of 500 watts each are used as a light source. A linedrawing printed on both sides is used as an original. The laterallyreversed electrostatic image of the original resulting on the zinc oxidecoating is made visible by dusting with a double toner consisting of aresin powder (toner) dyed with carbon black, and kieselguhr. The tonerconsists of a low melting point polystyrene-colophony mixture to whichcarbon black and preferably also the organic dye Nigrosin spiritsoluble(Schultz Farbstotftabellen, No. 985) have been added. The constituentsare melted together, ground and then separated into fractions by airsieving, since a uniform particles size is desirable for producing theimages. A toner with particle sizes ranging from 8l5,u is very suitable,for example. This toner is mixed with kieselguhr preferably in theproportion of 1:2 by weight.

The power image which was produced in this manner is transferred onto apaper printing foil. The paper printing foil consists of a paper basewhich is coated with a hydrophilic colloid, for example gelatin, casein,carboxymethyl cellulose, or polyvinyl alcohol in which a filler, forexample clay, is finely distributed. The hydrophilic coating is coatedwith a solution consisting of 100.0 parts by volume of ethylene andglycol-monomethyl ether, 5.0 parts by weight of Z-methylbenzimidazoleand 4.0 parts by weight of a ketone resin (Kunstharz EM, made byRheinpreussen G.m.b.H., Homberg/Niederrh., Germany) and is then dried.The thus prepared paper printing foil is placed onto the electrostaticpowder image with its coated side and subjected to the electric field ofa corona discharge whereby the powder image is transferred onto thepaper printing foil. Then, the two foils are separated and the powderimage is fixed by heating for 30 seconds in a drying cupboard atapproximately 160 C.

The obtained image is converted into a printing plate by wiping it overwith a 2.0% by weight solution of phosphoric acid. The areas not coveredby the toner are thereby removed, so that'the water-accepting layer isexposed. Images which are completely free of background are obtained.The printing plate can then 'be used for printing in an offset printingmachine.

Example 2 A paper foil is coated with a zinc oxide suspension, asdescribed in Example 1 and after drying of the coating, anelectrophotographic image is produced as described in Example 1. Thepowder image is transferred onto an aluminum foil previously coated witha solution consisting of 100.0 parts by volume of ethyleneglycolmonomethyl ether, 5.0 parts by weight of naphthalene-1,8-di carboxylicacid (naphthalic acid), and 2.0 parts by weight of a styrene copolymercontaining carbonyl groups, having a decomposition range of ZOO-210 C.and a specific gravity of 1.15-1.16 (Lustrex 820) and then dried. Thepowder image is transferred onto this material as described in Example1, and is fixed by heating to approximately 180 C. For conversion into aprinting plate, the image is wiped over with a solution containing, byweight, 40.0% methanol, 10.0% glycerin, 45.0% glycol and 5.0% sodiumsilicate. The areas of the coating which are not covered by the tonerare removed. The water-accepting layer is thus exposed, whereas theprinting areas, i.e., the co-called image areas, accept greasy ink, sothat the printing plate thus obtained can be used for printing in anoffset machine.

Example 3 5.0 parts by weight of 2,5-bis-(4'-diethylamino-phenyl-(1))-l,3,4-oxadiazole, 5.0 parts by Weight of a phenolmodified syntheticresin (Rhenophen and 0.01 g. of Rhodamine B are dissolved in 100.0 partsby volume of benzene, and a mechanically roughened aluminum foil iscoated with the solution. After drying, the coat-ing is provided with anegative electric charge by means of a corona discharge. Anelectrophotographic image is obtained as described in Example. 1.

The powder image is transferred onto a paper printing foil in anelectric field. The paper printing foil, which has a hydrophiliccoating, is provided with a covering layer before transferring theimage. For this purpose, a solution consisting of 100.0 parts by volumeof water and 8.0 parts by weight of the sodium salt of2,3-dihydroxynaphthalene 6 sulfonic acid is applied to thewater-accepting coating of the paper printing foil on a whirl-coater andthen dried.

The powder image transferred onto the coating is fixed at approximatelyC. and may be converted into a printing plate by wiping the coating overwith water. The coating, consisting of the sodium salt of2,3-dihydroxy-naphthalene-6-sulfonic acid, is thus removed from theareas not covered by toner together with the kieselguhr which adheres toit loosely.

In order to increase the water-accepting properties of the non-imageareas further, the image is wiped over with an 0.5% solution ofphosphoric acid. The printing plate thus obtained can be used forprinting in an offset machine.

Example 4 A reversed positive electrostatic charge image is obtained onan aluminum foil, which was vapor treated with selenium in known manner,and is made visible with a developer consisting of a toner and glassballs covered with a synthetic resin. The powder image is transferredonto a paper printing foil, thus producing a correct image of theoriginal. The paper printing foil which is intended for transferpurposes, is provided with a coating prepared as follows: 50.0 g. of2-(p-aminostyrene)-5- amino-benzimidazole and 40.0 g. of synthetic resinEM are dissolved in 1000.0 parts by volume of ethyleneglycol monomethylether. A hydrophilic coating on the paper printing foil is coated withthis solution by machine application and dried.

After transferring the powder image onto the material, the image isfixed by heating at 180 C. for 30 seconds. Then, it may be convertedinto a printing plate by wiping over with a 2%, by weight, solution ofphosphoric acid.

It will be obvious to those skilled in the art that many modificationsmay be made within the scope of the present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications.

What is claimed is:

1. A process for preparing a printing plate which comprises forming afusible powder image on an electrophotographic plate, transferring thepowder image to a covering layer which is stable to heat and ing ahydrophilic surface, treatment, and removing the is on a supporthavpowder image.

2. A process according to claim 1 in which the support is paper.

3; A process according to claim 1 in which the support is 'metal.

4. A process according to claim 1 in which the support is aluminum. i

5. A process according to claim 1 in which the hydrophilic surface is acoating of a hydrophilic colloid.

6. A process according to claim 1 in which the solvent is an aqueoussolution of phosphoric acid and the covering layer is soluble in an acidsolution.

7. A process according to claim 1 in which the solvent is water and thelayer is soluble in water. Y

8. A process according to claim 1 in which the covering layer comprises2-methyl-benzimidazole and "a ketone resin. 7 r Y 9. A process accordingto claim 1 in which the-covering layer comprisesnaphthalene-1,8-dicarboxylic acid and a styrene copolymer containingcarbonyl groups.

10. A process aecording to claim 1 in which the covering layer comprisesthe sodium salt of 2,3-dihydroxynaphthalene-6-sulfonic acid.

11. A process according to claim 1 in which the covering layer comprisesZ-(p-aminostyrene)-5-aminobenzimidazole and a synthetic resin. I

.12. A transfer material for use in the preparation of planographicprinting plates which comprises a support having a hydrophilic surface,and a covering'layer which is stable to heat on the hydrophilic surface,the covering layer being soluble in an aqueous solvent which does notdissolve the hydrophilic surface.

13. A transfer material according to claim 12 in which the support ispaper. 7

14. A transfer material according to claim 12 in which the support ismetal.

. 15. A transfer material according to claim 12 in which the support isaluminum. r

16. A transfer material according to claim 12 in which the hydrophilicsurface is a coating of a'hydrophilic colloid.

17. A transfer material according to claim 12 in. which the solventis-an aqueous solution of phosphoric acid andthe covering layer issoluble in an acid solution.

18. A transfer material according to claim 12in which i the solvent iswater and the layer is soluble in water.

19. A transfer material according to claim 12 in which the coveringlayer comprises"2-methyl-benzimidazole and a ketoneresinv u 20. Atransfer material according to claim 12in which the covering layercomprises'napthalene=LS-dicarboxylic acid and a styrene copolymercontaining carbonyl groups.

21. A transfer material according to claim' 12 in which i the coveringlayer comprises the sodium salt of 2,3.-dihydroXynaphthalene-6-sulfonicacid.

22. A transfer material according toclaim 12 in which 7 the coveringlayer comprises Z-(p-ar'ninostyren'e)-5-aminobenzimidazole and asynthetic resin.

References Cited by the Examiner FOREIGN PATENTS 210,374 9/1957Australia.

DAVID KLEIN, Primary Examiner.

1. A PROCESS FOR PREPARING A PRINTING PLATE WHICH COMPRISES FORMING AFUSIBLE POWDER IMAGE ON AN ELECTROPHOTOGRAPHIC PLATE, TRANSFERRING THEPOWDER IMAGE TO A COVERING LAYER WHICH IS STABLE TO HEAT AND IS ON ASUPPORT HAVING A HYDROPHILIC SURFACE, FUSING THE IMAGE BY HEATTREATMENT, AND REMOVING THE COVERING LAYER IN THE NONIMAGE AREAS BYTREATMENT WITH AN AQUEOUS SOLVENT WHICH DOES NOT DISSOLVE THEHYDROPHILIC SURFACE ON THE FUSED POWDER IMAGE.